From Long wire to Yagi
Long wire (II)
Every amateur radio working on HF knows this aerial : hang a very long wire over 1l long as high as possible (from 6 to 30m high), attach the far-end to an insulator screwed to a pole or around a tree (you can use a bowline knot), and connect the other side to an impedance transformer (balun) linked to a coaxial cable of any length to your transceiver : you have made a long wire antenna, also named Beverage.
Indeed, this very simple and cheap wire antenna was invented by Harold H. Beverage, W2BML, from RCA in 1919. This long wire merits well its name. In 1921, Beverage installed a receive Beverage 14-km long between Riverhead in New York and Chatam in Massachusetts.
Today, the long wire is mainly used by amateurs (licensed as well as listeners) who do not want to invest much money in their aerial and who are not DX addicts, although a long wire well tuned works fine in DXing too. Some ranchers even used their fence (made of barbed wire) to work local stations !
Except in receive where a simple electric wire will give excellent results, like the cabling system of your house, for emission it is important to select a cable relatively thick but not for the same reason.
Indeed, in an electric wire at high frequencies most of the current flows around the outer surface of the wire : it is the skin effect. Therefore, a large wire (large gauge #) is needed to avoid losses and any risk. Usually amateurs use a #18 AWG (Ø 1 mm) or #16 AWG (Ø 1.3 mm) for 100-200 W and #14 AWG (Ø1.63 mm or #12 AWG (Ø 2 mm) up to 1.5 kW. Here is a conversion page between gauge and metric.
Note that a 30-m segment of RG-8 or RG-213 coaxial cable sustains a power up to 2.8 kW at 14 MHz, while a RG-58 or RG-6 sustains 0.8 kW (see this calculator).
Installed in a few minutes, this type of antenna radiates best on any frequency for which its overall length is equal or greater to 1/2l. So a 20m long wire will work perfectly to transmit from the 40 to the 10m band with a low SWR (< 2:1).
Calculator to use : Attenuation & Power Handling, Times Microwave systems
However, as a long wire displays usually a very high impedance, mainly when short (including windom and other shortened wire antennas), like a dipole you need to reduce the extremely high impedance to a range that can be matched with your antenna tuner (external A.T.U. or built-in in your transceiver).
Note that if you connect a long wire to a coaxial to make the link to your transceiver, one of the two conductors of the feed line will be useless (usually the external braid). This unbalanced system is called a "end-fed Zepp". To work properly, the second conductor or rather the ground side of the antenna tuner must be connected to a ground system made of radials, but very few amateurs take the time to install it and work without optimizing their installation. We will see on the next page that the FD4 or Windom antenna, an off-centered dipole, takes advantage of this principle.
Recall that if your built-in antenna tuner shows a very low SWR, it can be sky high to the antenna. To get confirmation, you must use an external SWR-meter, if possible connected close to the antenna feed point. In this way you will know the true values of forward and reflected powers and your real SWR.
Without matching the antenna impedance with the one of the transceiver, don't be surprised if you get a very high SWR at the antenna and unable to work DX stations over a few thousand kilometers : most of your RF signal is waste as heat with high currents flowing in your system. Avoid to work this way or you might damage your transceiver and be injured if you touch connectors.
To match the transceiver impedance, often limited to a narrow ranges close to 50W, to the one of the antenna that can easily reach 450- 600W for a long wire, you need a matching section in between. You can use an open-wire feed line with a 6:1 balun, and a coaxial to get both a 50W impedance at the transceiver antenna terminal and a very low SWR close to 1:1 on any band. Now your antenna will radiate all the output power, 100 W PEP instead of 50 or maybe only 20 W; two or five more power is worth well some tuning, Hi !
This solution requesting some accessories and changing somewhat the original long wire design, another method is to use an MTFT magnetic balun like the ones displayed at right.
This accessory is a resistance transformer with a ratio of 10:1; you will get no more problem to reduce the extremely high impedance of the wire to a value close to the one supported by your antenna tuner. This magnetic balun allows to get a SWR better than 1.5:1 on all HF bands, including WARC.
At last, there is the solution of connecting several wires of different lengths (at least 6m long) to the same antenna terminal. The resulting antenna impedance should be reduced because all impedances will be added in parallel.
Whatever the solution used to match impedances, this simple wire gives astounding results for what it costs. Here is an example that surprised my correspondents by the quality of the audio (mainly due to the Kenwood TS-570D transceiver and the strength of the signal (performance shared between the transceiver and the antenna).
I built a long wire using a roll of 15m of ordinary stranded electrical wire (about 1mm thick) protected with a black PVC jacket for discretion. Living in the country, on top of hills, 250m over Meuse valley, I tightened this simple wire outdoor at 4 m high over the garden, attaching one end to a tree, the other side to an 6:1 balun connected to a short length of RG-58 coax linked to my transceiver antenna terminal.
The fire angle was approximatively NE-SW with a main lobe at 90° due to its low height over ground. Believe me or not, used in SSB with 50 W PEP, less than 30 W out (average reading), I worked with ease on HF bands all European countries and even some more. In CW this long wire could work the world !
Used during one week in summer 2004, this modest antenna worked fine taking into account its setup and the poor propagation conditions. I worked stations from Ireland to European Russia and Turkey to Portugal, so up to 2200 km away at daytime with a signal between 56 and 59+. Leaving Europe was another affair but I was able to reach the Canary islands, Kazakhstan (3000 km) and Asiatic Russia (5000 km) using sometimes the grayline.
But there is no secret. Due to its too short length and low output power, in SSB this "long wire" was unable to reach Canada, Middle East, Central Africa or Asia for example. But recall that at this time the ionosphere was not in good shape what also affected its performance, but doesn't explain all.
Indeed, with the same low power, if you can install a longer Beverage (say 40 m long), place it 0.5-1 l high, this long wire can compete against a dipole or a vertical with ground plane, and even give better results if it is very long (> 5-10l).
The best proof, using a long wire 2.5 times longer (40m long and hanging it twice higher (6m high only), at the first calls on the 20m band I reached Algeria, Canada and French Guyana (7500 km) with signals up to 58.
This confirms two points. The first and essential, feeding (matching) correctly your antenna improves much its performance, allowing it to radiate correctly into space all the transmitter power. Second, extending the length of a long wire or a dipole antenna over 1l, and placing it higher over the ground improves much its radiation pattern in additing a low incidence lobe allowing DX activities. In fact the longer the long wire, the sharper the lobes, with an optimal length that can exceed 10l (200 m long to work on 20 meters).
Most if not all long wires operate like a transmission line terminated in a open circuit; they are not terminated with a non-inductive resistance. Such long wires are also named "standing wave antennas". What can we say about the other designs ?
A long wire 1l long placed 1l high shows a front-to-back ratio of about 3 dB, thus 0.6 dB more than a 1/2l dipole placed at the same height.
In practice both azimuthal and elevation radiation patterns of a long wire placed 20m high and working on the 20m band show from 2 to 8 lobes if we respectively extend its length from 1/2l to 8l.
A 20m long wire (1l) placed 1l high, shows two lobes at 15 and 45° of elevation as displayed at right. Its azimuthal radiation pattern shows a double-8 shape (35°, 140°, 220 and 320°) where a dipole of the same length shows a simple ¥ (90 and 270°).
In this configuration the advantage is already to the long wire over the dipole. A 100m long wire (5l) placed 1l high shows a main lobe at 10° of elevation plus 4 narrower ones at approximatively 40, 50, 70 and 80°. Its horizontal pattern shows up to 16 secondaries lobes where a dipole shows always a simple ¥.
For a same length, if a long wire displays the same advantages as a dipole (G5RV or Lévy), its only drawback is to interfere with most home devices (TV, phone, radio, etc). These RFI occur because the end of the antenna displays usually a high impedance (thus high currents too) and travel close to power, phone and other lines.
To suppress these HF interferences, you can install - besides a good ground - a counterpoise made of a 1/4l-wire or longer that will run at ground level. You can also install it inside your house. Another solution is to configure the antenna in inverted-L (G) which end will be connected to an antenna tuner, itself connected to a ground. The vertical segment should be as long as the long wire or over 8 m long. Its role is to create a sink for the HF. This way, your antenna system will display a low impedance that will suppress the interfering HF and it will show an excellent radiation pattern.
To read : Your first antenna – the half-wave dipole, SRGB
Inverted-L, V-beam, rhombic and loop
The gain of a long wire can be optimized by tilting it of a few tens of degrees or bending one segment at 90°. However, the benefit can be nulled and even negative due to the proximity of the ground. Several variantes of the straight long wire can be thus successfully tested, depending on your free space.
An inverted-L (G) is a hybrid antenna between the vertical and the long wire. Like the inverted-V (see next page) this is a half-wave antenna. The feedline is connected to a first vertical segment attached to an insulating pole (using a tree, a fishing rod, a mast made of fiberglass or any other non conductive material) then runs horizontally to a second fixing point. An inverted-L must be fed at the end, otherwhise, if you feed it by the center, the feedline will couple with the vertical section of the antenna and will create interferences.
As we just told, an inverted-L performs rather well if the vertical section can be 8 m or more long, placed away from the building wall, and if the vertical end is not too close to the ground. Complementary, the combination of horizontal and vertical polarizations increases its sensitivity to DX signals as polarization from far emitters signals can vary considerably from minute to minute according to the propagation and the way that radio waves are reflected through ionospheric layers and cross the geomagnetic field. Like the inverted-V, the inverted-L works thus better than a dipole at long distance but is less good at short distance due to its vertical component. This double polarization has been successfully used to design the Windom antenna that we will review on next page.
To get more gain and directivity you can also combine several long wires together, using parallel wiring, a V-shape (V-beam) or a horizontal diamond shape (rhombic) to increase the intensity of some major lobes and cancel others. Only drawback, you need space.
Using for example 2 legs 1l long, tight 1l high and forming an angle of 75°, you increase the two opposite horizontal lobes (at 90 and 270°) at decrease of about 15 dB the intensity of the two perpendicular lobes (at 0 and 180°). If legs are terminated with a 500 to 800W non-inductive resistance, there are no more standing waves, and you get a very directive V-beam which displays about 2 dB more gain than a 1/2l dipole and only 4 dB below a 4-element Yagi. But remember that placing a long wire (or even a beam) too close to the ground (say below 1/2l or 10m high) will drastically affect its radiation patterns on both E and H planes.
Recall that the usual feeding method of a V-beam is using a quarter-wave matching section. An open-wire line (ladder line) connected to a balun or a MTFT magnetic balun with optionally an antenna tuner are as many alternatives.
At last, name the wire loop, to not confuse with the magnetic loop (see next page). It is a loop antenna a full-wave long (up to 160 m) on the working frequency, and multi-band. It is feeded at the base with an antenna tuner. Placed horizontally over 8 m high (most users install it in trees up to 20m high), it can display a square or delta shape and has not to be perfectly flat-top. Many amateurs consider it as the most efficient wire antenna, all the more compared to verticals ! The loop antenna come in several models. But those working so-called without antenna tuners are less efficient and loss their multi-band properties.
NB. We will review the Beverage when we will discuss about wire antennas for listeners as due to its conditions of use it is first of all dedicated to listening purposes.
As explained in the page dealing with wire antennas for listeners, if you have no place left to install a long wire antenna outdoors you can tight it in a restricted loft space, e.g. in the attic or in an elevated spare room. As such the wire is very sensitive to artificial noises and if you experiment severe QRM replace the lower part of the aerial with a coaxial cable which braid is connected to the ground. Practically using a 50W RG-58 coax (insulation black colored) the grounding can change the QRM from S-9 to S-4 or even less, allowing weak signals to be heard.
In smaller rooms up to 16 m2 you can strung a similar aerial around the room at ceiling level, at the condition to use at least 12 m of wire, the longer the best. However do not expect miracles, mainly in SSB. You might work stations in bordering countries and will be able to ragchewing in regional QSOs up to 1000 km away or so but probably not further.
The main reasons for which indoor antennas do not work well are multiples :
- The antenna is placed at a low height above ground in terms of HF wavelengths
- The antenna is usually small in terms of HF wavelengths
- The antenna works close to sources of RFI, it can couple to electrical wiring and other gutter and besides lossy dielectric materials like masonry, plaster and wood.
- The antenna cannot be rotated.
Among its advantages list the next facts:
- The antenna is invisible from the outside (like stealth !)
- The antenna is out of weathering effects (wind, rain, ice, etc)
- The antenna can be made of low resistance material as it only needs to support its own weight
- The supporting structure is in place
- The investment is reduced compared to an outdoors installation that requires a mast, fixings and often foundations
- The antenna is accessible all time what simplifies its tuning.
Some amateurs installed a shortened HF beam in their attic too. As we saw in the pages devoted to portable installations, several 3-element beams offer indeed a turning radius less than 3 m (e.g. Cushcraft MA5B, Butternut HF5B, TGM MQ-36SR). However, set up a beam, even short, in an attic or in a spare room is like oblige a fish to live out of the water ; this is unthinkable.
Not only a beam is bulky but most of the time the parasitic elements (the reflector and directors) will couple to the house wiring or the roof structure will cause dielectric loading of the parasitic elements which, for once, deserve well their name; they will generate QRM. This is mainly the case if the room in which you install the antenna but also the near rooms contain conductors near a quarter wave in length or longer at the working frequency (5m to work on the 20m band).
Unfortunately I bet that your house is full of electrical wires and plumbing measuring at least 5m long. You will experiment losses and your antenna will radiate less or no energy at all into space. In these conditions an external antenna tuner can help you to fine tune the impedance of your system.
So the best alternative should be to install an horizontal or vertical loop antenna (see next page). With a diameter that does not exceed 1m in HF, this solution has been experimented successfully by several amateurs. Kim Stenson, W4KVS, for example related his experience on the 6-m band in the pages of QST in March 2004. He concludes that the M2HO 6-m loop set up in the attic has given him good signals but his short Cushcraft 6-m beam, also installed in his attic for a while, pulled in the weakest signals better.
Of course all these considerations are mainly valid for a transmission antenna. For receiving all these solutions work very well
There is only one major constraint installing your transmission antenna indoors, this is the danger of RF radiation to not disregard. This is mainly the case using a single-wire feed line that is not well balanced and creates a potential radiation hazard, with a short Yagi that concentrates all the energy in a narrow beam, and with a magnetic loop that generates a strong magnetic field. Here are some useful recommendations.